Subsea production systems can range in complexity from a single satellite well with a flowline linked to a fixed platform or an onshore installation, to several wells on a template or clustered around a manifold, and transferring to a fixed or floating facility, or directly to an onshore installation. Subsea production systems can be used to develop reservoirs, or parts of reservoirs, which require drilling of the wells from more than one location. Deep water conditions, or even ultra-deep water conditions, can also inherently dictate development of a field by means of a subsea production system, because traditional surface facilities such as on a steel-piled jacket, might be either technically unfeasible or uneconomical due to the water depth.
Subsea hydrocarbon. e.g., oil and gas, extraction has an exceptionally safe record and has been going on for approximately 100 years. Oil and gas fields reside in deep water and shallow water around the world. When they are under water and tapped into for the hydrocarbon production, these are generically called subsea wells, fields, projects, development, or other similar terms. Subsea production systems can be used to develop reservoirs, or parts of reservoirs, which require drilling of the wells from more than one location.
The development of subsea oil and gas fields requires specialized equipment. The equipment must be reliable enough to safe guard the environment, and make the exploitation of the subsea hydrocarbons economically feasible. The deployment of such equipment requires specialized and expensive vessels, which need to be equipped with diving equipment for relatively shallow equipment work, i.e., a few hundred feet water depth maximum, and robotic equipment for deeper water depths. Any requirement to repair or intervene with installed subsea equipment is thus normally very expensive. This type of expense can result in economic failure of the subsea development.
On occasion, it is necessary to lower a string of pipe from a drilling platform or drilling barge or other above water structure or vessel down through the water and into the previously drilled portion of the subbottom borehole. For example, during the drilling of the well bore, it becomes necessary to pull the drill string out of the hole and back aboard the drilling platform or vessel for purposes of changing the drill bit. Then, the drill string is lowered through the water and into the subbottom well bore for purposes of continuing the drilling operation.
The pipe lowering operation is difficult for various identifiable reasons. For example, a string of pipe is to be lowered from a floating vessel, down through several hundred feet of water and into the mouth of a subbottom well bore on the order of eight inches in diameter. Obviously, there is a problem in getting the bottom end of the pipe string or drill string to hit the mouth of the well bore. The dilemma is similar to threading a needle from a distance of several hundred feet. The problem is further complicated by the fact that a string of pipe having a length of several hundred or several thousand feet is flexible and is readily subject to being deflected by movement of the vessel or underwater currents.
There are no satisfactory means of directing the bottom end of a string of pipe to the mouth of a subbottom well bore, other than by moving the surface ship or platform and rotating the pipe in the hope that the pipe string and the mouth of the well bore will come into alignment with one another. As a consequence, directing the bottom end of a string of pipe to the mouth of a subbottom well bore is very time consuming at best and may, in some cases, be impossible to accomplish.